Swing-type excavation machines, for example hydraulic excavators and front shovels, require significant hydraulic pressure and flow to transfer material from a dig location to a dump location. These machines direct the high-pressure fluid from an engine-driven pump through a swing motor to accelerate a loaded work tool at the start of each swing, and then restrict the flow of fluid exiting the motor at the end of each swing to slow and stop swinging of the work tool.
One problem associated with this type of hydraulic arrangement involves efficiency. In particular, the fluid exiting the swing motor at the end of each swing is under a relatively high pressure due to deceleration of the loaded work tool. Unless recovered, energy associated with the high-pressure fluid may be wasted. In addition, restriction of this high-pressure fluid exiting the swing motor at the end of each swing can result in heating of the fluid, which must be accommodated with an increased cooling capacity of the machine.
One attempt to improve the efficiency of a swing-type machine is disclosed in U.S. Pat. No. 7,908,852 of Zhang et al. that issued on Mar. 22, 2011 (the '852 patent). The '852 patent discloses a hydraulic control system for a machine that includes an accumulator. The accumulator stores exit oil from a swing motor that has been pressurized by inertia torque applied on the moving swing motor by an upper structure of the machine. The pressurized oil in the accumulator is then selectively reused to accelerate the swing motor during a subsequent swing by supplying the accumulated oil back to the swing motor.
Although the hydraulic control system of the '852 patent may help to improve efficiencies of a swing-type machine in some situations, it may still be less than optimal. In particular, there may be no way to recover energy from pressure spikes during a discharge event of the accumulator disclosed in the '852 patent. Likewise, no method of charging the accumulator during a neutral swing event is disclosed. Finally, the accumulator of the '852 patent may have limited ability to recover energy at the end of a swinging deceleration event, when swinging motions have slowed significantly.
The disclosed hydraulic control system is directed to overcoming one or more of the problems set forth above and/or other problems of the prior art.